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'''OpenGL extension EXT.depth_clamp |
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This module customises the behaviour of the |
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OpenGL.raw.GLES2.EXT.depth_clamp to provide a more |
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Python-friendly API |
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Overview (from the spec) |
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Conventional OpenGL clips geometric primitives to a clip volume |
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with six faces, two of which are the near and far clip planes. |
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Clipping to the near and far planes of the clip volume ensures that |
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interpolated depth values (after the depth range transform) must be |
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in the [0,1] range. |
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In some rendering applications such as shadow volumes, it is useful |
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to allow line and polygon primitives to be rasterized without |
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clipping the primitive to the near or far clip volume planes (side |
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clip volume planes clip normally). Without the near and far clip |
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planes, rasterization (pixel coverage determination) in X and Y |
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can proceed normally if we ignore the near and far clip planes. |
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The one major issue is that fragments of a primitive may extend |
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beyond the conventional window space depth range for depth values |
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(typically the range [0,1]). Rather than discarding fragments that |
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defy the window space depth range (effectively what near and far |
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plane clipping accomplish), the depth values can be clamped to the |
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current depth range. |
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This extension provides exactly such functionality. This |
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functionality is useful to obviate the need for near plane capping |
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of stenciled shadow volumes. The functionality may also be useful |
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for rendering geometry "beyond" the far plane if an alternative |
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algorithm (rather than depth testing) for hidden surface removal is |
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applied to such geometry (specifically, the painter's algorithm). |
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Similar situations at the near clip plane can be avoided at the |
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near clip plane where apparently solid objects can be "seen through" |
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if they intersect the near clip plane. |
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The official definition of this extension is available here: |
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http://www.opengl.org/registry/specs/EXT/depth_clamp.txt |
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''' |
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from OpenGL import platform, constant, arrays |
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from OpenGL import extensions, wrapper |
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import ctypes |
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from OpenGL.raw.GLES2 import _types, _glgets |
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from OpenGL.raw.GLES2.EXT.depth_clamp import * |
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from OpenGL.raw.GLES2.EXT.depth_clamp import _EXTENSION_NAME |
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def glInitDepthClampEXT(): |
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'''Return boolean indicating whether this extension is available''' |
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from OpenGL import extensions |
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return extensions.hasGLExtension( _EXTENSION_NAME ) |
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